Wonderful Cryptography Topics for a motivational "introduction to cryptography" lecture

The following are some suggested topics for a motivational "introduction to cryptography" lecture for a non-specialized audience. The choice criteria are as follows: convey ideas of some technical or theoretical depth; provide a feeling for the scope of cryptographic research; maximize novelty and intellectual stimulus; motivate things by relating them to common objects and tasks. Of course, the specific choice of topics and pace would depend on the target audience.

If you have any suggestions for additions or corrections, please contact me.

How to sign your mail without really meaning it
Deniable signatures, as special case of
ring signatures. The problem with deniability when
the recipient can plausibly deny knowledge of his own secret
key leads to:

How to prove things without revealing your sources
The concept of zero-knowledge, exemplified by Kid Cryptography and graph 3-colorability (or Hamiltonicity).

Romantic applications of
playing cards
The concept of secure multiparty
computation, exemplified by the 5-card protocol for secure
evaluation of AND (consider using a lazy suzie instead of oblivious
cuts). Any function
can be securely computed with a sufficiently large deck of cards.

Voting using PEZ candy
More secure computation, using a PEZ dispenser: the 3-candy
protocol for AND and the 13-candy protocol for 3-party
voting. Any function
can be securely computed given enough candy!

CrypTool
CrypTool is an interactive "cryptographic laboratory", developed as an open-source project initiated by Deutsche Bank. It offers visualization of concepts and data in many fundamental cryptographic objects and methods, including: popular encryption algorithms and protocols, several cryptanalysis methods (from breaking Vigenère ciphers to lattice attacks on RSA), side-channel attacks and random-number generators. See its screenshots for some examples.

Acknowledgments.
I am indebted to Boaz Barak, Alex Biryukov, Moni Naor, Tal Rabin and
Adi Shamir for
valuable suggestions, and to Yossi Vardi and the rest of the KinnerNet
2005 participants for providing the perfect motivation for preparing
my first such talk.